The present invention relates to ultrasonic transducer and measurement systems of the type wherein an electrically actuated signal source, typically a piezoelectric crystal, is mounted in a mounting assembly fixed to a housing or wedge, or fixed directly to a conduit, to propagate ultrasonic signals through a medium flowing in the conduit. It particularly relates to such transducer and measurement systems wherein the medium has a low density, such as a gaseous medium, or to systems wherein size of the conduit or signal path length through the medium raise considerations of crosstalk.
In these circumstances, the amount of signal energy which can be received through the medium is relatively small or difficult to distinguish. For example, the signal propagates through the gas with a velocity different from and generally much slower than its propagation velocity through the solid structure of the conduit, so it can be difficult to find a suitable timing window in which the received signal can be dependably distinguished from ringing or other energy propagated directly through the conduit walls.
To some extent the problem of signal strength can be addressed by appropriate impedance matching and the use of a large-area diaphragm to couple the crystal to the medium. However, suitable isolation remains a problem, particularly in view of the relatively large amount of energy contained in the solid-path noise band.
One approach to this problem has been discussed in the inventor's U.S. Pat. No. 5,179,860 entitled "Snap-On Flow Measurement System". In that patent, specifically with reference to FIG. 15A thereof, a construction is shown involving acoustically massive rings or a spiral body interposed in the solid body acoustic path between the transmitting and receiving crystals. In applicant's U.S. Pat. No. 5,275,060 entitled "Ultrasonic Transducer System with Crosstalk Isolation", a number of related constructions are shown, in which abrupt impedance changes occur along a path that includes thin-walled conduit, housing, mounting; or stand-off elements. The full disclosure of that latter patent is hereby incorporated by reference herein. The present disclosure is directed to related constructions, further isolation structures, and different practical embodiments of transducer isolation and mounting structures.